1. Field of the Invention
The present invention relates to a liquid crystal composition, and more particularly to a liquid crystal composition suitable for liquid crystal display devices of the twisted nematic mode in which the multiplex drive scheme is employed.
2. Description of the Prior Art
Recently, the enlargement of the information content of display a device is needed in the field of liquid crystal display devices. Liquid crystal display devices of the matrix display type are being supplied more and more because they are more appropriate for the enlargement of the information content than liquid crystal display devices of the segment display scheme which have previously been used. The increase in the number N of multiplexed lines of the multiplex drive in the matrix display scheme is also demanded in order to develop the diversification of display further.
A matrix display is usually driven with the optimized amplitude selecting method. Then, liquid crystal materials applicable to liquid crystal display devices of the matrix display type with large display capacity should have sharp threshold characteristics or good contrast characteristics for a small voltage difference near the threshold voltage. This can easily be understood as for liquid crystal display panels of the X-Y matrix display as follows. If they are driven with the optimized amplitude selecting method, the ratio of the effective voltage V.sub.rms (on) in the selected elements to the effective voltage V.sub.rms (off) in the unselected elements is expressed in the following equation: ##EQU1## It is apparent in this equation that .alpha. decreases to 1 when N is increased up to infinity. In other words, the difference between V.sub.rms (on) and V.sub.rms (off) decreases with an increase in N. The contrast of the liquid crystal display also depends on the angle at which a man views the display, and the viewing angle dependence of the threshold characteristics should be weak for the display device with a wide viewing angle. Accordingly, liquid crystal materials suitable for large display capacity should show sharp contrast for the small difference in the effective applied voltage or should have sharp threshold characteristics against the effective applied voltage.
However, prior art liquid crystal materials do not have threshold characteristics good enough for matrix drive with a relatively large N, and this causes troubles such as the lowering of the display contrast and the narrowing of the effective viewing angle.